mfd: lpc_ich: Change Avoton to iTCO v3

The register layout of the Avoton is compatible with the iTCO v3
register layout.

Signed-off-by: Peter Tyser <ptyser@xes-inc.com>
Tested-by: Rajat Jain <rajatjain@juniper.net>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Lee Jones <lee.jones@linaro.org>